Immediately after the First Vatican Council in 1870, some German theologians organized a meeting of theologians from various universities and lay people to protest against the new dogma of the infallibility and universal jurisdiction of the bishop of Rome (Königswinter Declaration 14.8.1870). A second meeting drew up a formal manifesto in which it declared that the "First Vatican Council" defining the infallibility was not a true council, for it was neither free, nor unanimous, nor ecumenical. After the opponents were all excommunicated by the Vatican, a bishopric was established in Germany, which chose a bishop who was consecrated in 1873 by the Dutch Old-Catholic bishop of Deventer (Netherlands). Reforms long needed were made and carried out with success, such as a synodal structure of the church, the liturgical use of German, and permission for clerical marriage. The diocese of the Old-Catholics was recognized as a "Catholic Diocese" by the king of Prussia and the grand dukes of Hessen and Baden.

The Old-Catholics are among the pioneers of the ecumenical movement. A first Old-Catholic Congress was held in Munich in 1871, attended by members of Anglican, Orthodox and Lutheran churches. In 1874-75 two conferences were held in Bonn invited by the standing committee of the synod, to promote Christian unity. In 1889 the Old-Catholic bishops in Europe agreed to form the Union of Utrecht. Since 1931 full communion is practised with the Anglican churches ("Bonn Agreement"), and more recently with the Philippine Independent Church, the Spanish Reformed Episcopal Church and the Lusitanian Church of Portugal. Dialogue with the Orthodox churches continues. An agreement on eucharistic hospitality was signed with the Evangelical Church in Germany (EKD) in 1985. In May 2009, the International Roman Catholic – Old Catholic Dialogue Commission published the final report on its several years of consultation aiming at communion between the Roman Catholic and the Old Catholic Church. The new document, titled "Kirche und Gemeinschaft" (Church and Communion), is more than a consensus paper and marks significant progress.

Priests are trained at the Old-Catholic seminary of the university of Bonn and the diocesan seminary "Johanneum". Since 1994 all the ordained ministries are open to women. The first women priests were consecrated in 1996.